Abstract
A poly-row branched spike (prbs) barley mutant was obtained from soaking a two-rowed barley inflorescence in a solution of maize genomic DNA. Positional cloning and sequencing demonstrated that the prbs mutant resulted from a 28 kb deletion including the inflorescence architecture gene HvRA2. Sequence annotation revealed that the HvRA2 gene is flanked by two LTR (long terminal repeat) retrotransposons (BARE) sharing 89% sequence identity. A recombination between the integrase (IN) gene regions of the two BARE copies resulted in the formation of an intact BARE and loss of HvRA2. No maize DNA was detected in the recombination region although the flanking sequences of HvRA2 gene showed over 73% of sequence identity with repetitive sequences on 10 maize chromosomes. It is still unknown whether the interaction of retrotransposons between barley and maize has resulted in the recombination observed in the present study.
Highlights
The architecture of branched inflorescences in grasses depends on the developmental fate of primordia and axis orientation[1]
Genetic analysis indicated that the mutant phenotype was caused by a recessive gene, which has an epistatic effect on Vrs[111]
The prbs was initially mapped to the centromere of the short arm of chromosome 3H11,12, a location similar to that of vrs[4]
Summary
The architecture of branched inflorescences in grasses depends on the developmental fate of primordia and axis orientation[1]. The barley domestication gene Vrs[1], located on the long arm of chromosome 2H, encodes a homeodomain-leucine zipper (HD-Zip) transcription factor that suppresses the development of lateral spikelets in two-rowed barley. The Int-c gene modifies lateral spikelet fertility in barley, and can influence the phenotypic effect of the Vrs[1] locus[7]. Vrs[4] is an ortholog of the maize inflorescence architecture gene RAMOSA2 (RA2), which encodes a transcriptional regulator that contains the lateral organ boundaries (LOB) domain. Expression analyses by mRNA in situ hybridization and microarray approaches showed that Vrs[4] is expressed very early during inflorescence development and controls the row-type pathway through Vrs[1] by negatively regulating the lateral spikelet fertility in barley. We report on a new mutant, poly-row and branched spike (prbs) obtained by soaking a two-rowed barley inflorescence in maize genomic DNA from a single cross hybrid[9,10], and characterize its genetics, report its positional cloning, and analyze its origin
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